Does Cow’s Milk Cause Early Puberty?

Au Pairs and Nannies Can Serve More Than Just Organic Milk

A debate has been raging for years over whether girls are now reaching puberty earlier than ever before. The debate escalated in 1997, when the journal Pediatrics published a study of 17,000 girls by Dr. Marcia Herman-Giddens of the University of North Carolina that found outward signs of puberty that precede menstruation — budding breasts and pubic hair — were hitting younger. Now scientists are trying to unravel why.

Nannies, au pairs, and mothers constantly say that cow’s milk is to blame. This theory that hormones (steroids) in cows milk causes early puberty is merely hypothesized, but not proven. (Not that someday it might be clinically studied and proven).

In fact, the man-made bovine growth hormone that is blamed on early development in girls does not survive pasteurization. That’s right. The steroid is destroyed before children drink the milk!

Plus, the Food and Drug Administration (FDA) scientists have concluded that eating foods with slightly higher levels of rbGH does not affect human health. This is because the amount of rbGH that is in milk or milk products as a result of treatment of the animals is insignificant compared to the amount of growth hormone that is naturally produced by our bodies.

Also, rbGH is a protein hormone and is digested into smaller fragments (peptides and amino acids) when eaten.

The rbGH hormone used on dairy cattle is effective in promoting growth in cows, but does not work in humans. Scientists know that rbGH is not recognized as a hormone by human cells.

Some speculate that good nutrition may lead to early puberty. Others speculate chemicals in plastics could cause early breast development.

But, so far the only cause that has been proven is that high mass body weight produces more estrogen causing overweight girls to start puberty earlier than other girls.

The reason that fat is the top theory is that the fatter you are, the more your body can convert adrenal hormones into the female sex hormone estrogen.

Overweight children’s blood harbors more insulin, which also influences maturation.

Scientists even are studying whether the protein leptin, produced by fat cells, influences glands that produce sex-related hormones. See “Fat cell metabolism in different regions in women. Effect of menstrual cycle, pregnancy, and lactation,” by M Rebuffe-Scrive in The Journal of Clinical Investigation.

“It does not mean that every overweight girl is going to enter puberty earlier, but on average they do,” says Herman-Giddens, the study’s author and child health specialist.

“It has been long known that if you are overweight as you grow up, you are more likely to begin puberty early,” said Aviva Must, Ph.D., associate professor of Public Health and Family Medicine at Tufts University School of Medicine in Boston and lead author of the study, published in the September issue of the journal of Pediatrics. “Girls who are overweight are more likely to have early menarche, or start their period, before age 12.”

But Dr. Must also explains that although overweight girls are more likely to start their periods earlier than their peers who are at or below normal weight, early menstruation is not by itself a risk factor for later obesity, according to the study.

Elizabeth Chang, staff writer for the Washington Post, wrote in her Oct. 7, 2003 article “Tempest in a Glass: Synthetic Hormones in Milk Don’t Speed Puberty, Say Experts:

“Could hormones meant to make cows give more milk lead to early puberty, as some parents fear? On its face, it sounds plausible enough. But government and pediatric health experts say there are no scientific data to back up such an assertion. For one thing, they say, rBGH [man-made bovine growth hormone] does not survive pasteurization. And even if it did, they add, it has absolutely no effect on human growth…

For years, pediatricians have viewed age 11 as the mean age of breast development… In 1997 a landmark analysis of 17,000 U.s. girls led by University of North Carolina professor Marcia Herman-Giddens showed that many American girls were beginning to show secondary sexual characteristics between ages 9 and 10… But the changes documented in Herman-Giddens’s study cannot be attributed, even in part, to artificial bovine growth hormone for one important reason: The data for her study were collected in 1992 and 1993, before rBGH was available for dairy herds in the United States. Another problem with the rBGH and early puberty theory: Children today drink markedly less milk than they did a generation or two ago.”

The American Council on Science and Health stated in their June 2001 publication “The Role of Milk in Your Diet:

“Experts aren’t sure whether girls really are entering puberty earlier. If they are, the most likely explanation is that today’s girls are heavier than their mothers were at the same age. Puberty tends to occur earlier in heavier girls.

There is no research demonstrating that milk or dairy products play a role in early puberty. Milk has always contained hormones in very small amounts; their presence is not a result of any changes in animal husbandry practices. Today’s girls drink less milk than their mothers did. Thus, it seems very unlikely that milk is responsible for any change in the age at which girls enter puberty.”

The benefits of drinking milk far outweigh the risks. Although there have been no clinical studies proving that cow’s milk encourages early puberty in girls, the fact remains future studies may. Plus, serving children organic milk certainly does not hurt them. Nannies, au pairs, and parents do not need to be scared to serve children cow’s milk.

Do you serve children only organic milk?


  1. I acutally studied this in college. I worked as a nanny during college and have continued to until I can find a job in my field. There is a breast cancer program at the school I studied at and they also found there is no proof that the hormones given to dairy cow's affect the cow's milk humans drink. But they did find a problem with hormones in the beef, the actual meat from the cow.Although studies have not shown the hormones given to cattle is passed down in milk, organically raised meat is the only safe meat to eat. Free of chemicals, sprayed feed, antibiotics, and hormone-injected growth stimulators, organic, grass-fed beef is by far healthier and more nutritious than the commercial kind. There is also no proof that pesticides on vegetables cause cancer. I still prefer organic because common sense tells us to eat foods without pesticides.The European Union has banned hormone-treated American beef. For children, eating hormone-laced meat on a regular basis seriously increases their estrogen exposure.Although there is no proof of hormones being passed down in cow's milk, could you blame a parent that can afford organic milk not to buy organinc milk? I think the article above is correct in saying that caregivers do not have to be scared if only regular (non-organic) milk is available because it is safe to drink. But, I think organic beef is the only safe beef to eat. Nannies and au pairs need not worry about either type of milk though.

  2. My dad boss is a pedicatrician and I just asked him and he said it's true what you write.Amazing because everyone I know just think it is true – that there is no question that steroids in milk cause early puberty. My dad boss just confirmed it's not the case.I asked him why mom boss buys only organic milk then? He said doesn't hurt. Not a battle worth arguing with her.Also, the children buy milk at school and it isn't organic and she does not care. Interesting because we try to buy organic fruit, but she says just wash with dish soap and rinse really well and that should be good enough. When farmers aren't putting pesticides on their cows. Does pesticides on the grass they eat become a problem though?Dad boss says likely chemical sensitivity and allergies and asthma aggravated by pesticides, not likely steroids given diary cows.An aha moment for me. Thanks for enlightening me and no I won't argue it with my mom boss. We can go right ahead buying organic if it makes her more comfortable.

  3. It is difficult because what if future studies show that steroids in milk are a problem in the future? Sort of common sense to choose organic everything when possible, but not to stress-out if you can't find organic either. It is also amazing that so many nannies just assume this is a fact, when it is just a theory.Taylor Vero Beach FL

  4. You are brave to post this article because I think most mothers will disagree, but now I know they are wrong. Thanks for being brave enough to bring up the uncomfortable side of the topic. I think you will get a lot of grief because, like vaccines and autism, most parents have a really strong bias in what they believe – despite the facts not being proven. I even have been searching last night and now this a.m. before work for opposing views online and you are right. The overwhelming beleif of medical professionals is that cow's milk is safe to drink for humans and does not contain steroids that effect girls puberty in any way. I really did not know that. I truly think this is brave and the right thing to have brought to our attention.

  5. I am in my last sememster as a physician's assistant program about to graduate.I agree re: the hormones/overweight thing. I think people don't want to take accountability for their own health/diet/exercise, and so they want something else to blame when things go haywire because they are not taking care of themselves (ie premature puberty, diabetes, heart disease, the list goes on and on). I talk a lot with the drs I work with about that stuff, and I haven't met a single one yet who beleives that organic is the answer and that today's health problems are due to hormones in the milk/meat etc. Puberty is brought on by a weight threshold, plain and simple. Being overweight then causes insulin resistance in all the body's cells leading to diabetes, hih blood pressure, etc.. It's a very easy cycle to get out of though. Kids and people in general are very lazy today though. Kids sit around and play video games and are pretty sedentary, and the parents let them be that way. Many parents are lazy about eating and preparing healthy meals for themselves and their kids. So much junk and prepared foods and junk crap food! No video games in this house!! We have to lead by example too. The girls see me doing my exercise and working out and eating healthy, and so they do it to. I have to make sure it's instilled in them early so that they learn to enjoy it and make it a lifestyle.

  6. Actually, I have read that rbGH DOES survive the pasteurization process. Also, milk from cows fed grain rather than guess is nutritionally devoid. Each mammal makes milk for its own species. Cow's milk is meant for calves. Humans have adapted poorly to ingestion and absorption of other species' milk, for a reason – it's not meant for us! Drinking large quantities of other species' milk is a uniquely American phenomenon, other cultures do not ingest such large quantities, some none at all.

  7. "In fact, the man-made bovine growth hormone that is blamed on early development in girls does not survive pasteurization. That's right. The steroid is destroyed before children drink the milk!""Also, rbGH is a protein hormone and is digested into smaller fragments (peptides and amino acids) when eaten."You do see the obvious contradiction here, right? So… which is it?

  8. Anonymous wrote:"Puberty is brought on by a weight threshold, plain and simple. "This is plain and simply false. My own daughter's case is evidence to the contrary. At age 8 she is above the 95th percentile in height and about the 65th percentile in weight. That is, she is very slim. Yet she has benign precocious puberty. Since breastfeeding ended, she has drunk nothing but organic milk.When the cause of something unpleasant is unknown, people fill in the blanks with convenient myths. The truth is that nobody knows what causes early puberty.

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